Permeable measuring cell

ABSTRACT

A flow-through measuring cell having one inlet opening for entry of the fluid, and one outlet opening for exit of the fluid. A single measurement space is located between the inlet opening and outlet opening. A radiation measurement region is provided for measuring the interaction of the fluid in the measuring cell with electromagnetic radiation from outside the measuring cell. The radiation measurement region is bordered by two opposite windows of which one is intended for inlet and the other for exit of the electromagnetic radiation. The measuring cell has a positioning range with several operating positions with a different distance A, A′ between the windows into which the measuring cell can be set without rotation.

FIELD OF THE INVENTION

The invention relates to a flow-through measuring cell.

BACKGROUND OF THE INVENTION

To measure the interaction of electromagnetic radiation with fluids in ameasuring cell, there must be permeable and transparent windows in themeasuring cell for the region of the electromagnetic spectrum which isrelevant to the measurement. The windows must seal a measurement spaceof the measuring cell relative to the environment, even at possiblyhigher pressures. This applies especially to inline measuring cells.

In particular for absorption measurements it is necessary to knowexactly the resulting layer thickness or the optical path length alongthe beam path of the electromagnetic radiation in order to be able toevaluate the measured values accordingly.

In many measurement applications it is necessary to clean the measuringcell often and/or to make available another layer thickness. In thepast, different measuring cells were used for this purpose or variousinserts for different layer thicknesses were provided.

U.S. Pat. No. 5,905,271 discloses a measuring cell with a complexmechanical structure in which the adjustment of the optical path length,therefore of the distance between the windows, is enabled in a verysmall region (by compression of the seal 31 on the stop 22).

SUMMARY OF THE INVENTION

The object of this invention is to devise a measuring cell which can beeconomically produced and which can be flexibly used.

Advantageous developments of the invention are given in the dependentclaims. All combinations of at least two of the features given in thespecification, the claims and/or the figures also fall within the scopeof the invention. At the given value ranges, values within the indicatedlimits will also be considered to be disclosed as boundary values andwill be claimed in any combination. To avoid repetitions, featuresdisclosed for the system are also to be considered to be disclosed andclaimed for the device Likewise features disclosed for the device arealso to be considered to be disclosed and claimed for the system.

The invention is based on the idea of making at least one of the windowslocated in the beam path settable, or at any time adjustable, withoutadjustment attachments on the measuring cell or on the measuring cellbody along the beam path during installation so that (one-time) settingor adjustment of the distance A, A′ between the windows is enabled atleast in an adjustment state of the measuring cell, especially for agiven temperature range. In other words: The measuring cell has severaloperating positions to which the measuring cell can be set or adjusted.This measure makes it possible to produce a measuring cell with minimumcosts since a wide range of distances A, A′ (corresponds especially tothe optical path length of the measuring cell) along the adjustmentrange can be set, especially during installation. During or afterinstallation and setting, the window or windows can be fixed so thatadjustment is no longer necessary.

When an adjustment capacity is provided (thus without fixing of thewindows) it is no longer necessary to replace the measuring cell tochange the layer thickness or at least to replace an insert of themeasuring cell. The user can set the distance A, A′ within a positioningrange at will.

The construction of the measuring cell calls for the setting/adjustmentto be able to take place without rotation. A complex mechanism isavoided in this way. Stops for limiting the movement can also beomitted.

It is especially conceivable to provide the windows as claimed in theinvention in a basic form which can be produced especially easily.Shaping of the outside contour, especially of stops and the like, can beomitted. In particular the outside contour of the windows is flat orwithout shoulders or in any cross section rectangular along the beampath. Transversely to the beam path the window can have a circular crosssection with an identical diameter over the entire window length(optionally aside from a bevel on the face sides of the window). Thewindow, in one version which can be produced especially easily, has theshape of a round cylinder. Alternatively the simple basic shape can alsoconsist in a plate-shaped configuration with a cross section which isrectangular to the beam path.

In other words, the operating position can be set by application of acompressive force to the windows in the direction of the beam pathexclusively from outside of the measuring cell, optionally incombination with a spacer element between the windows to limit themovement. Exclusively from outside means that on the measuring cellitself there are no mechanical means for applying pressure.

In one advantageous embodiment of the invention it is provided that themeasuring cell after setting of a first operating position is adjustablewithin the positioning range, especially without mechanical positioningmeans attached to the measuring cell (1, 1′), preferably exclusively inthe direction of the opposite window.

To the extent the measuring cell is formed from plastic at least on thewindow receiver, especially the predominant part of the measuring cell,preferably essentially the entire measuring cell, economical productionof the measuring cell is possible. Moreover the measuring cell can bemade as a disposable measuring cell.

Moreover at least one of the windows can be made in a force fit/pressfit so that the distance A, A′ can be set along the force fit and atleast in the direction of the opposite window is easily adjustable bypressure from the outside. This simplifies the installation since withidentical measuring cells different optical path lengths can beimplemented. In the installation of the measuring cell the set distanceA, A′ (or the optical path length) can be fixed and identifiedaccordingly, especially by a coding of the measuring cell.

It is also conceivable as claimed in the invention that the operatingposition can be set or adjusted along one fit of the window or onewindow receiver which accommodates the window in the measuring cell,preferably by direct fitting of the window relative to the guide channelof the measuring cell or of the measuring cell body, which channel ismade especially as shaping of the measuring cell wall. Fitting takesplace relative to the inlet or outlet openings and has a tolerance atwhich the window at least during installation can be moved along thebeam path by applying pressure from outside the measuring cell.

At the same time the tolerance of the fit ensures sealing of themeasurement space relative to the vicinity of the measuring cell,especially without special sealing means (such as gaskets). The nominaldiameter of the fit is the same along the adjustment range.

In this connection one or both windows can be adjustable to one anotheralong their alignment, especially along one window receiving channelwhich corresponds to the outside contour of the window, preferably byfrictional engagement in the channel. To the extent the two windows areadjustable, a larger adjustment range can be implemented. The frictionalengagement is caused by the corresponding fit of the window or of thewindow receiver. The window receiver channel preferably has parallelchannel walls in the adjustment range.

According to another advantageous embodiment of the invention it isprovided that the positioning range extends from the smallest settabledistance A, A′ at least by a factor of 1.5, especially at least by afactor of 2, preferably at least by a factor of 3 of the smallestsettable distance A, A′. The larger the adjustment range, the moreflexibly the measuring cell can be used.

According to one alternative embodiment of the invention it isadvantageously provided that at least one wall which borders themeasurement space can be flexible deformed along the alignment of thewindows and a spacer element for fixing the plane of the window at adistance which is dictated by the choice of the spacer element outsidethe measurement space can be inserted between the windows. An especiallylarge adjustment range can be implemented by these embodiments.

Here it is especially advantageous if the wall is made as bellows.

An independent invention is a system composed of the above describedmeasuring cell with several spacer elements of different length forsetting a distance A′ which is defined by the respective spacer element.This makes it possible to offer a set with different stages for definedoptical path lengths or distances A′. The user can use the set forcorrespondingly different application conditions without keeping variousmeasurement cells in reserve.

To the extent the spacer element/elements are made as U-shaped sections,the installation of the measuring cell, especially during adjustment, isfacilitated. It is especially advantageous that it is not necessary tointervene in the measurement space or to open the measurement space whenthe distance A changes.

To the extent at the same time the wall is located, especially fixed onone of the windows, forming a seal, to seal the measurement space, thewall performs a double function, as a result of which additionalcomponents such as gaskets, etc. are superfluous.

Other advantages, features and details of the invention will becomeapparent from the following description of preferred exemplaryembodiments and using the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a cross sectional view of a first embodiment of a measuringcell as claimed in the invention,

FIG. 2 shows a cross sectional view of a second embodiment of ameasuring cell as claimed in the invention,

FIG. 3 a shows a perspective view of a third embodiment of a measuringcell as claimed in the invention,

FIG. 3 b shows a cross sectional view of the embodiment according toFIG. 3 a along one sectional plane A_(S) and

FIG. 3 c shows a cross sectional view of the third embodiment along onesectional plane B_(s) from FIG. 3 a.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

In the figures the same elements and elements with the same functionsare identified with the same reference numbers.

FIG. 1 shows a measuring cell 1 through which a fluid can flow and whichhas the measurement space 4 which is bordered by a measuring cell body5. A fluid flows through the measurement space 4; the interaction of thefluid with electromagnetic radiation, especially light from a lightsource, is to be measured.

For this purpose there is a radiation measurement region 6 on whichelectromagnetic radiation is routed through the fluid transversely tothe flow direction of the fluid from a radiation source which is notshown, especially a light source. The electromagnetic radiation ismeasured on the opposite side.

In the beam path (beam direction transversely to the flow direction)there are windows 7, 8 in order to allow the passage of theelectromagnetic radiation through the measurement space 4 into thefluid. The windows 7, 8 are each routed in the guide channels 11, 12whose inside contour corresponds to the outside contour of the windows7, 8 so that there is a fit between the windows 7, 8 and the respectiveguide channel 11, 12. This enables an adjustment of the windows 7, 8along the inside contour of the guide channels 11, 12 so that a distanceA between the windows 7, 8 can be set or adjusted. This distance Acorresponds especially to the optical path length.

The windows 7, 8 are formed from quartz glass, while the measuring cellbody 5 consists of plastic in this exemplary embodiment. The dimensionsof the outside contour of the windows 7, 8 and of the inside contours ofthe guide channels 11, 12 are dimensioned such that the windows 7, 8 atroom temperature, therefore at roughly 20° C., can be moved along theguide channels 11, 12 by sliding, even under process conditions,therefore at elevated temperatures, especially greater than 40° C.,preferably greater than 60° C., there being frictional engagementbetween the outside contour of the windows 7, 8 and the respectiveinside contour of the guide channels 11, 12 so that the windows 7, 8seal the measurement space 4 relative to the environment even atpressures, especially greater than 3 bar. The tolerance of the fits ismade accordingly, the different expansions of the different materialsbeing considered.

To do this it is advantageously provided as claimed in the inventionthat the windows 7, 8 have a thickness D which is greater than usual ata ratio to a width B of the windows 7, 8. Preferably the ratio D to B isat least 1:10, especially at least 1:5, preferably at least 1:3, evenmore preferably at least 1:2.

It is also conceivable as claimed in the invention to fix the windows 7,8 after setting of a distance A in the production/ installation of thewindows 7, 8 so that adjustment of the windows is precluded. This isespecially advantageous when using the measuring cell 1 as a disposablemeasuring cell.

In the second embodiment which is made very similarly to the firstaccording to FIG. 2, in contrast to the embodiment as shown in FIG. 1,there is one window receiver 9, 10 each for accommodating the windows 7,8. The window receivers 9, 10 are made tubular with an inside contourwhich corresponds to the outside contour of the windows 7, 8 so that thewindows 7, 8 are fixed in the window receivers 9, 10. The windows 7, 8are each fixed in the window receivers 9, 10 on the end of the windowreceiver 9, 10 which points toward the measurement space 4, especiallyflush with the window receivers 9, 10. The window receivers 9, 10 withtheir outside contour correspond to the guide channels 11, 12 such thatthe above described interaction between the windows 7, 8 and the guidechannels 11, 12 applies as in the first embodiment according to FIG. 1.Both the guide channels 11, 12 and the window receivers 9, 10 as well asthe window receivers 9, 10 and the windows 7, 8 have a fit to oneanother. The fit can be made such that mutual displacement is possiblefor only one of the two fits. Advantageously the two fits can be mademovable, as a result of which a larger adjustment range can beimplemented.

By the window receivers 9, 10 on their ends facing away from the windows7, 8 projecting over the measuring cell body 5 or over the guidechannels 11, 12, the adjustment of the distance A between the windows 7,8 is simplified, especially when the distance A is increased. This isbecause the window receivers 9, 10 can be gripped on their ends whichproject above the measuring cell body 5 or the guide channels 11, 12.Using the dimensions of the window receivers 9, 10 along the beam path,the distance A, therefore the optical path length, can be measured andcomputed and can accordingly be automatically set. In this case it isadvantageous if the fit between the guide channels 11, 12 and the windowreceivers 9, 10 is made movable.

The statements on the first embodiment also apply analogously to thesecond embodiment.

FIG. 3 a shows a measuring cell 1′ with a measuring cell body 5′ whichconsists predominantly of flexible material, especially rubber. Thefluid which is to be measured is routed via an inlet opening 2 into ameasurement space 4′ and leaves the measurement space 4′ via an outletopening 3 which is shown in FIG. 3 b. The inlet opening 2 and the outletopening 3 have process connections for incorporating the measuring cell1′ into the process line, therefore for inline measurement.

Transversely to the flow direction of the fluid there is a radiationmeasurement region 6 in which the interaction of the fluid withelectromagnetic radiation is measured.

The radiation enters the measurement space 4′ through a window 7′ andemerges from the measurement space 4′ through a window 8′ which islocated opposite. The electromagnetic radiation is produced by aradiation source which is not shown outside the measuring cell 1′ and isrouted transversely to the flow direction of the fluid through themeasurement space 4′ and the windows 7′, 8′. On the opposite side,therefore under the window 8′ and outside the measuring cell 1′, theradiation is detected by a corresponding measuring apparatus, by theinteraction with the fluid along the optical path length between thewindows 7′, 8′ the changes which identify the fluid being detectable.

An important aspect of detection is the optical path length which existsby a distance A′ between the window 7′ and the window 8′.

One wall 13 of the measuring cell body 5′ which is made as a peripheralwall is attached to the side of the window 7′ which points toward themeasurement space 4′, especially in the center of the window 7′ therebeing a passage opening 14 so that the electromagnetic radiation canenter the measurement space 4′. A corresponding wall 15 which is made asa peripheral wall and which is located opposite is likewise madeflexible. It is accordingly fixed on the window 8′ on one side of thewindow 8′ which points toward the measurement space 4′ and has a passageopening 16 for exit of the electromagnetic radiation through the window8′.

The measuring cell body 5′ or the measuring cell 1′ is fixed by at leastone, in this exemplary embodiment two U-shaped spring clips 17, 18transversely to the flow direction of the fluid. The spring clips 17, 18extend around the measuring cell body 5′ and the windows 7′, 8′ from theside of the windows 7′, 8′ facing away from the measurement space 4′.

To fix the distance A′ between the windows 7′, 8′ there is at least one,in this exemplary embodiment two spacer pieces 19, 20 which are clampedoutside the measuring cell body 5′ as rigid spacers between the windows7′, 8′, in particular by the clamping action of the spring clips 17, 18.

Accordingly by replacing the spacer pieces 19, 20 and optionally thespring clips 17, 18 an adjustment range of the distance A′ which islimited by the shape of the walls 13, 15 can be implemented so thatthere is a system consisting of a standard measuring cell 1′ and a setof spring clips 17, 18 and corresponding spacer pieces 19, 20.

It is advantageously provided as claimed in the invention that thereplacement of the windows 7, 7′, 8, 8′ is not necessary for adjustingthe distances A, A′. The spring clips 17, 18 and spacer pieces 19, 20which are intended for a defined distance A′ can be understood as setswith defined identifications so that replacement can be managedcorrespondingly easily.

The spacer pieces 19, 20 each have one installation opening 21, 22,especially in which the spacer pieces 19, 20 are made as U-shapedsections so that adjustment of the distance A′ is enabled withoutdecoupling of the measuring cell 1 from the process lines.

The function of the spring clips 17, 18 according to one advantageousembodiment which is not shown can be integrated into the spacer piecesby the windows 7′, 8′ being able to be received into the spacer pieces.The spacer pieces can have corresponding receivers, especially pluggrooves, on their tops and bottoms.

REFERENCE NUMBER LIST

-   1, 1′ measuring cell-   2 inlet opening-   3 outlet opening-   4, 4′ measurement space-   5, 5′ measuring cell body-   6 radiation measurement region-   7, 7′ window-   8, 8′ window-   9 window receiver-   10 window receiver-   11 guide channel-   12 guide channel-   13 wall-   14 passage opening-   15 wall-   16 passage opening-   17 spring clip-   18 spring clip-   19 spacer piece-   20 spacer piece-   21 installation opening-   22 installation opening

1. A flow-through measuring cell with: an inlet opening (2) for entry ofthe fluid, an outlet opening (3) for exit of the fluid, a, especiallysingle, measurement space located between the inlet opening (2) andoutlet opening (3), a radiation measurement region (6) for measuring theinteraction of the fluid in the measuring cell (1, 1′) withelectromagnetic radiation from outside the measuring cell (1, 1′), theradiation measurement region (6) being bordered by two opposite windows(7, 7′, 8, 8′), of which one is intended for inlet and the other forexit of the electromagnetic radiation, characterized in that themeasuring cell (1, 1′) has a positioning range with several operatingpositions with a different distance A, A′ between the windows (7, 7′, 8,8′) into which the measuring cell (1, 1′) can be set, especially fixed,without rotation.
 2. The measuring cell as claimed in claim 1, whereinthe measuring cell (1, 1′) after setting of a first operating positionis adjustable within the positioning range, especially withoutmechanical positioning means attached to the measuring cell (1, 1′),preferably exclusively in the direction of the opposite window (7, 7′,8, 8′).
 3. The measuring cell as claimed in one of the preceding claims,wherein the measuring cell (1, 1′) is formed at least in part,especially predominantly, from plastic and/or rubber.
 4. The measuringcell as claimed in one of the preceding claims, wherein the operatingposition can be set or adjusted along one fit of the window (7, 8) orone window receiver (9, 10) which accommodates the window (7, 8) in themeasuring cell (1, 1′).
 5. The measuring cell as claimed in one of thepreceding claims, wherein one or both windows (7, 8) can be adjusted orset to one another along their alignment, especially along one guidechannel (11, 12) which corresponds to the outside contour of the window(7, 8), preferably by frictional engagement in the channel.
 6. Themeasuring cell as claimed in one of the preceding claims, wherein thepositioning range extends from the smallest settable distance A, A′ atleast by a factor of 1.5, especially at least by a factor of 2,preferably at least by a factor of 3 of the smallest settable distanceA, A′.
 7. The measuring cell as claimed in one of the preceding claims,wherein there is direct fitting of the windows (7, 7′, 8, 8′) relativeto the respective guide channel (11, 12) of the measuring cell or ofmeasuring cell body (5, 5′), which channel is made especially as shapingof the measuring cell body.
 8. The measuring cell as claimed in claim 1to 3 or 6, wherein at least one wall (13, 15) which borders themeasurement space (4′) can be flexibly deformed along the alignment ofthe windows (7′, 8′) and a spacer element (19, 20) for fixing the window(7′, 8′) at a distance which is dictated by the choice of the spacerelement (19, 20) outside the measurement space (4′) can be insertedbetween the windows (7′, 8′).
 9. The measuring cell as claimed in claim7, wherein the wall (13, 15) is made as bellows.
 10. The measuring cellas claimed in one of claim 7 or 8, wherein the wall (13, 15) for sealingthe measurement space (4′) is located, fixed underneath, on one of thewindows (7′, 8′), forming a seal.
 11. A system of a measuring cell (1′)as claimed in claim 7, 8, or 9 with several spacer elements (19, 20) ofdifferent length for setting a distance A′ which is defined by therespective spacer element (19, 20).
 12. The system as claimed in claim10, wherein the spacer elements (19, 20) are made as U-shaped sections.